Field of the Invention
The present invention relates generally to methods and systems for measuring multiple soil properties across a field, and to agricultural planters that vary seeding rates and planting depths on-the-go during planting operations.
Description of the Related Art
Soil moisture is a major driver of crop production, particularly in arid regions. Soil moisture varies spatially within fields due to soil texture, topography, crop usage, irrigation patterns, and various other variables.
Fixed, semi-permanent moisture sensors (e.g., gypsum blocks and neutron probes) and manually inserted sensors (e.g., TDR, capacitance) have been used for many years to monitor soil moisture levels in agricultural fields. However, these moisture sensors do not capture the spatial variability as their expense and manual deployment make it unfeasible to collect enough measurements to produce a spatially accurate map of soil moisture.
Variable rate irrigation allows limited irrigation water supplies to be applied at different rates in different areas of a field. For example, variable rate irrigation can be used to apply more irrigation water to zones of a field where water holding capacity is lower or where crop use or productivity is expected to be greater. Fixed moisture sensors are often used in fields with variable rate irrigation. However, the use of fixed moisture sensors does not link soil moisture with soil properties that affect water-holding capacity and crop usage of water.
Systems and methods are known for measuring soil electrical conductivity (EC) and soil color (reflectance). For example, the Applicant's copending application Ser. No. 13/277,208 filed on Oct. 19, 2011, for an invention titled “MOBILE SOIL OPTICAL MAPPING SYSTEM” provides a system for measuring soil reflectance values and using the soil reflectance data to determine and map soil organic matter (OM). For another example, Applicant's copending Application No. 61/774,559 filed on Mar. 7, 2013, for an invention titled “METHOD AND SYSTEM FOR CLASSIFYING SOIL PRODUCTIVITY” provides a system for analyzing and using data collected from on-the-go soil EC and soil reflectance sensors. The contents of these prior applications are hereby incorporated herein by reference.
Soil EC relates to soil texture and soil moisture. Soil optical measurements relate to soil OM and soil moisture. Increasing levels of soil moisture increase soil's ability to conduct electricity and make the soil appear darker. The presence of soil moisture, especially when its variations do not spatially correlate with soil texture and soil OM, can confound soil EC and optical sensing of soil texture and soil OM. Soil EC and soil color sensors have been developed and are being used to relate to soil texture and organic matter, but no system or method exists for accounting for the contribution of soil moisture.
Typical planting depths for agricultural crops, such as corn, are 1.5 to 2.5 inches. The grower's objective is to place seed into warm, moist soil at a consistent depth to achieve uniform emergence. Germination and emergence are optimized when depth is consistent and seeds are placed in the optimal combination of warm and moist soil.
However, moisture and temperature vary spatially within fields and within the top 3 inches due to soil texture, topography, crop usage, irrigation patterns, residue cover, and a variety of other factors. Growers must occasionally compromise one factor for another, e.g., planting deeper into colder soil than desirable in order to have seed in moist soil.
There is a need for a method and system for on-the-go sensing of soil moisture, soil EC and other properties, and for using those measurements to improve various processes, such as variable rate irrigation, soil mapping, and planting.